The present invention relates to a processing system, such as a plasma etching system, and a temperature control method for controlling an object to be processed, in such a processing system.
In conventional processes for fabricating semiconductor devices and LCD substrates, various processing systems, such as plasma etching systems, are used. For example, in a plasma etching system, a predetermined process gas is activated as plasma in a vacuum processing chamber to etch an object to be processed, such as a semiconductor wafer or glass substrate supported on a supporting table. During the processing, the object to be processed is maintained at a predetermined temperature in order to inhibit the temperature rise of the object due to the plasma, or to enhance the aspect ratio in etching, or to arrange the etched shape.
The temperature control for the object to be processed is generally carried out by a cooling mechanism provided on the supporting table. The cooling mechanism adopts a construction for feeding a refrigerant into a refrigerant circulating passage extending in the supporting table and for absorbing heat by the refrigerant to cool the object to be processed. The refrigerant in a refrigerant tank temperature-controlled by a cooling circuit is fed into the refrigerant circulating passage by a pump, and the refrigerant returned from the refrigerant circulating passage is temperature-controlled by the cooling circuit to be fed into the refrigerant tank. The temperature of the refrigerant in the refrigerant tank or the refrigerant fed from the tank into the refrigerant circulating passage is monitored to carry out a temperature control so that the temperature of the refrigerant is a predetermined temperature.
However, the temperature of the refrigerant is controlled regardless of the heat quantity loaded on the object to be processed, i.e., the heat quantity absorbed by the refrigerant in the refrigerant circulating passage. Therefore, if the heat quantity applied to the object to be processed is increased by the plasma processing, the temperature of the object rises until heat balance is saturated. As a result, there is a problem in that the object to be processed can not be uniformly processed.
It is therefore an object of the present invention to provide a novel and improved processing system and a method for controlling the temperature of the system, the system and method being capable of solving the above described problem and other problems.
According to the present invention, there is provided a method for controlling the temperature of an object to be processed, on a supporting table in a processing system, the system comprising a processing vessel including the supporting table having therein a refrigerant circulating passage, and a temperature control circuit for controlling a heat quantity and/or a flow rate of a refrigerant circulating in the refrigerant circulating passage, wherein inlet and outlet temperatures of the refrigerant in the refrigerant circulating passage are detected, and the heat quantity and/or the flow rate of the refrigerant in the temperature control circuit is controlled on the basis of an actual differential value, which is a difference between the inlet and outlet temperatures, to control the temperature of the object on the supporting table.
According to this method, the actual difference value, which is the differential value between the outlet temperature as the temperature of the refrigerant having absorbed heat in the refrigerant circulating passage, and the inlet temperature as the temperature of the refrigerant before absorbing heat, is in proportion to the heat quantity per unit time, the heat quantity being absorbed by the refrigerant from the object to be processed (via the supporting table). Therefore, by controlling the heat quantity and/or the flow rate of the refrigerant in the temperature control circuit on the basis of its actual differential value, the temperature control can be carried out so as to maintain the object at a constant temperature, in accordance with the variation in heat quantity applied to the object during the processing. Thus, the processing system can uniformly process the object by maintaining the constant temperature of the object.
In this method, preferably, a target differential value, which is a theoretical difference between the inlet and outlet temperature of the refrigerant in the refrigerant circulating passage, is previously determined in accordance with a process in the processing system, and the heat quantity and/or the flow rate of the refrigerant in the temperature control circuit is controlled so that the actual differential value follows the target differential value.
According to such a construction, on the basis of the target differential value, which is the theoretical difference between the inlet and outlet temperature according to the processing, the temperature can be controlled so that the actual differential value is substantially equal to the target differential value. Therefore, it is possible to precisely control the temperature of the object.
In this case, more preferably, a relationship between the target differential value and a target return temperature of the refrigerant returning to the temperature control circuit is previously determined in accordance with the process in the processing system, and the heat quantity and/or the flow rate of the refrigerant is controlled so that an actual return temperature of the refrigerant returning to the temperature control circuit follows the target return temperature.
According to such a construction, if the relationship between the target differential value and the target return temperature is set so that the value obtained by subtracting the target differential value from the set temperature of the object is equal to the target return temperature, the temperature of the refrigerant can be surely controlled according to the variation in heat quantity during the processing, by controlling the heat quantity and/or the flow rate of the refrigerant so that the actual return temperature follows the target return temperature.
In this case, if the heat quantity and/or the flow rate is controlled while carrying out the feedback so that the actual differential value follows the target differential value, it is possible to more precisely control the temperature of the object.
In place of the target return temperature, the target feed temperature may be used. That is, a relationship between the target differential value and a target feed temperature of the refrigerant being fed from the temperature control circuit may be previously determined in accordance with the process in the processing system, and the heat quantity and/or the flow rate of the refrigerant may be controlled so that an actual feed temperature of the refrigerant being fed from the temperature control circuit follows the target feed temperature.
According to another aspect of the present invention, there is provided a processing system comprising: a processing vessel for processing therein an object to be processed; a supporting table, provided in the processing vessel, for supporting thereon the object; a refrigerant circulating passage formed in the supporting table; and a temperature control circuit for controlling a heat quantity and/or a flow rate of a refrigerant circulating in the refrigerant circulating passage, the processing system further comprising: an inlet temperature detector for detecting an inlet temperature of the refrigerant in the refrigerant circulating passage; an outlet temperature detector for detecting an outlet temperature of the refrigerant in the refrigerant circulating passage; and a controller for controlling the heat quantity and/or the flow rate by the temperature control circuit on the basis of an actual differential value which is a difference between the inlet and outlet temperatures detected by the temperature detectors.
According to this processing system, the inlet and outlet temperatures, which are the temperatures of the refrigerant before and after absorbing heat in the refrigerant circulating passage, are detected by the inlet temperature detector and the outlet temperature detector. The actual differential value, which is the differential value between the outlet and inlet temperatures, is in proportion to the heat quantity per unit time, the heat quantity being absorbed by the refrigerant from the object via the supporting table. Therefore, by controlling the heat quantity and/or the flow rate of the refrigerant in the temperature control circuit by means of the controller on the basis of the actual differential value, the temperature control can be carried out so as to maintain the object at a constant temperature, in accordance with the variation in heat quantity applied to the object during the processing. Thus, the processing system can uniformly process the object by maintaining the constant temperature of the object.
In this system, preferably, further comprise a return temperature detector for detecting a return temperature of the refrigerant returning to the temperature control circuit, the controller controlling the return temperature on the basis of the actual differential value.
In place of the target return temperature, the target feed temperature may be used. That is, the processing system may further comprise a feed temperature detector for detecting a feed temperature of the refrigerant being fed from the temperature control circuit, the controller controlling the feed temperature on the basis of the actual differential value.
In above described systems, preferably, the temperature control circuit controls the heat quantity and/or the flow rate of the refrigerant via an inverter-controlled electrical driving unit.
Thus, the operation of the electrical driving unit can be finely controlled to stably control the heat quantity and/or the flow rate of the refrigerant. It is also possible to prevent a rush current from being generated by the on/off of the electrical driving unit and so forth, so that it is possible to reduce electric power consumption.